1. Field of the Invention
The present invention generally relates to semiconductor devices, and more particularly, the present invention relates to a semiconductor wafer polishing slurry and to a chemical mechanical polishing (CMP) method using such a slurry.
2. Description of the Related Art
Chemical mechanical polishing (CMP) planarization methods are widely employed in a variety of processes used to manufacture semiconductor devices. CMP can be used to planarize a single material layer, such as CMP of an interdielectric layer or metal interdielectric layer, or to polish materials having two or more layers, such as CMP in shallow trench isolation (STI) process. In the case of polishing materials having two or more layers (such a layer to be polished and a polishing stop layer), it is generally necessary that the CMP process exhibit high selectivity between the layers.
For example, when an insulating material such as a silicon dioxide layer (SiO2 layer) is planarized, generally a silicon nitride layer (Si3N4 layer) is used as a polishing stop layer. When present CMP techniques are employed in which the chief ingredient of the slurry is silica, the removal selectivity of SiO2:Si3N4 is known to be about 4:1 in a blanket wafer. This relatively low removal selectivity reduces the process margins and necessitates very fine CMP process control.
There is thus a desire for a CMP slurry that exhibits an improved removal selectivity between a layer to be polished and a silicon nitride polishing stop layer.
An objective of the present invention is to provide a CMP slurry that exhibits an improved removal selectivity between a layer to be polished and a silicon nitride polishing stop layer, and to provide a polishing method using such a slurry.
According to one aspect of the present invention, a CMP slurry includes quaternary ammonium compound which is a compound having the form of {Nxe2x80x94(R1R2R3R4)}+Xxe2x88x92, where R1, R2, R3, and R4 are radicals and Xxe2x88x92 is an anion derivative.
R1, R2, R3, and R4 of the quaternary ammonium compound can be an alkyl group or an alkanol group, and R1, R2, and R3 are generally a methyl group and R4 is an ethanol group. Preferably, the quaternary ammonium compound can be [(CH3)3NCH2CH2OH]Cl, [(CH3)3NCH2CH2OH]l, [(CH3)3NCH2CH2OH]Br, [(CH3)3NCH2CH2OH]CO3, or mixtures thereof.
The slurry can further include a pH control agent formed of a base such as KOH, NH4OH or (CH3)4NOH, or an acid such as HCl, H2SO4, H3PO4 or HNO3. Also, a pH control agent can include [(CH3)3NCH2CH2OH]OH.
The slurry can further include a surfactant such as cetyldimethyl ammonium bromide, cetyldimethyl ammonium bromide, polyethylene oxide, polyethylene alcohol, or polyethylene glycol.
According to another aspect of the present invention, a polishing method includes providing a semiconductor wafer having a silicon dioxide layer and a silicon nitride stop layer, and chemical mechanical polishing the silicon dioxide layer and the silicon nitride stop layer using above-described slurry.